Strangeloop president Joshua Bixby decided to take a look at Steve Souders' old claim that 80% of performance issues happen at the front-end. It turns out that for desktop browsers, that number is now at around 85%. But for mobile Web browsers, the number is more like 97%. He published the results here.
Regarding how large the mobile Web's front-end response time, Bixby wrote "I expected this number to be higher than the desktop number, but not this high."
And yes, before any asks, I'm quite sure that by iPad3 and iPad4 he means an iPad running iOS 3 and one running iOS 4.
I would have liked to have seen Opera Mini/Mobile on these lists, since it's supposed to do much of the rendering usually reserved for the front-end on the back-end. Then again, BlackBerry was supposed to start doing that and it doesn't seem to have done any better than the other browsers tested.
Bixby admits these tests are not the last word on the subject, and needs to conduct further tests - particularly comparing different carrier networks and network types.